Validate Multiple RadioButton Groups for Required Validation using CustomValidator in ASP.Net

Dear All,

I have Table inside which 4 Radio buttons and i need to validate the radiobutton i.e. user should select atleast one in the same group. If user selected any one from the four then there is no validation.

 <table>
<tr>
    <td><asp:RadioButton Id="rad1" RunAt="server" GroupName="Radq1" /></td>
    <td><asp:RadioButton Id="rad2" RunAt="server" GroupName="Radq1" /></td>
    <td><asp:RadioButton Id="rad3" RunAt="server" GroupName="Radq1" /></td>
    <td><asp:RadioButton Id="rad4" RunAt="server" GroupName="Radq1" /></td>
</tr>
</table>

Any help on this.

Thanks